In microscopy, there is a need for particularly high sensitivities of sensors for generating signals. In this way, an imaging quality may improve. Conventional large-area detectors, such as e.g. photomultipliers (PMTs), have a quantum efficiency of approximately 20%-50%, provided that these are, for example, implemented by means of GaAsP anodes. Such detectors have comparatively large sensitive areas (detection area) of the order of several mm2 or several tens of mm2.
In principle, sensors with a relatively high sensitivity are known. By way of example, avalanche photodiodes (APDs) and other silicon-based sensors which have a comparatively high quantum efficiency of e.g. 80-90% are known. Typically, this is obtained by way of a comparatively small detection area which, for example, may be circular with a diameter of approximately 100 μm. This corresponds to a detection area of the order of less than 0.05 mm2.
Confocal microscopy is a specific type of microscopy. Here, a portion of a specimen is typically illuminated and this illuminated portion is varied incrementally in various illumination steps. By way of example, a laser-scanning microscope (LSM) may be used to this end. A light intensity of the light reflected by the specimen or otherwise emitted, e.g. by way of fluorescence, may be detected by a corresponding detector device for each illumination step.
The detection of emitted light in a spectrally selective manner is known within the scope of confocal microscopy. This is necessary, particularly in fluorescence-based confocal microscopy. As a result, a particularly high information content may be obtained during imaging. By way of example, the spectrally sensitive detection may be achieved by the use of optical filters. The optical filters suppress a specific spectral portion more strongly than other spectral portions. By way of example, the optical filters may be tuned to a specific wavelength or embodied as a so-called graduated filter. However, the use of optical filters typically attenuates the intensity of the light, as a result of which a signal level is reduced. As a result, there may in turn be a reduction in the signal-to-noise ratio in the measured signal. This may reduce an accuracy of the measurement.
A further option for suppressing specific spectral portions for a spectrally selective detection is offered by the spatial-spectral decomposition of the light with a subsequent manipulation of the spectral components as desired; in this respect, see e.g. the publication DE 198 42 288 A1. Techniques in which the beam path of individual spectral portions of the light may be manipulated by way of mirrors are known; in this respect, see e.g. the publications EP 0 717 834 B1, EP 1 053 497 B1 and U.S. Pat. No. 6,255,646 B1.
The use of mirrors may be comparatively complicated and expensive. Further, such techniques are disadvantageous in that a selection of individual spectral portions of the light is effected in the collimated beam. This typically limits a spectral resolution.